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www.p exels.c om/ph oto/a-p erson-h olding -a-pro sth etic-arm -61533 45/ Artificial Limbs By Dr David Maddison VK3DSM Artificial limbs have been around since ancient times, but were typically just timber extensions attached to the stump of a remaining limb. Modern prosthetics are much better replacements for lost limbs and can even provide functional hands, capable of many tasks that a human hand can perform. M any people with ‘passive’ prosthetics (up to 44%) decide not to use their artificial limbs because of problems relating to weight, discomfort and lack of functionality, as described in the paper at https://pubmed.ncbi.nlm.nih. gov/33377803 Currently, no artificial limb can come close to emulating a natural one. Still, even a small increase of functionality for an amputee can lead to an enormous quality of life improvement. There have also been great advances in wearable ‘powered exoskeletons’, particularly to assist those with paralysis, muscle weakness or infirmity. They are also used for rehabilitation. New developments in materials science, 3D printing, electronics, batteries and artificial intelligence (AI) have made new, lighter-weight, more comfortable and more functional artificial limbs or exoskeletons possible. We will look at some of these, in particular those that involve the use of electronics rather than purely mechanical devices. A replacement limb should ideally appear natural, although it seems some users like the non-natural ‘cyborg’ look. The limbs should generally 14 Silicon Chip mimic nature as closely as possible, both for a natural appearance as well as intuitive and expected operation (degrees of freedom etc). Cost is also an important consideration, as the cost of a prosthetic limb can be significant. Connection to the body One of the most important concerns affecting patient comfort is the way the artificial limb is connected to the body. Rather than cumbersome belts, silicone rubber and gel materials are a much more comfortable fit of the prosthesis ‘socket’ to the limb stump. Comfort can be further enhanced with 3D scanning of the stump and corresponding 3D printing of the socket to get the best possible fit. Direct skeletal attachment of the prosthesis (‘osseointegration’) is another recent development, but is not suitable for all patients, as great care is needed for the area where the skin is penetrated. Control, sensing & feedback When the prosthesis is active, ie, it has some form of motor or motors built into it, there obviously must be a means to control it. This generally has to be simple and easy to learn or adapt to. Australia's electronics magazine Ideally, there should also be some means of sensing the position of the prosthesis in space and also to provide feedback to the user of limb activity such as grip force for a hand (proprioception). By having both control and sensing, an artificial limb can approach the utility of a real one. One of the most important aspects of controlling an artificial limb is to determine user intent. This is commonly done by attaching electrodes to the skin in the vicinity of the remaining nerves that would have been used to control the limb. The body still sends electrical impulses from the brain to those, as if the limb still existed. These can be interpreted to establish what the person wishes the limb to do. There are also other possible control methods, which we will discuss later. Beyond that, the next step is to interface directly to the nerves or even the brain, as in the case of Neuralink, a brain-computer interface. Proprioception Proprioception is the ability of a person to determine the location of parts of their body without having to look, as well as sensing the weight of siliconchip.com.au an object and forces exerted. While we are taught in primary school that there are five senses, we actually have between 22 and 33; proprioception is one of the more important ones, along with balance (via the inner ear), pain and temperature sensing. For more realistic prosthetic limb behaviour, it is important that proprioception is incorporated into the artificial limb. In the natural human body muscle spindles, Golgi tendon organs and skin receptors are all responsible for producing proprioception sensations. These allow us to sense changes in length, tension and deformation, as shown on the left in Fig.1. These same senses can be measured electronically by (for example) the number of revolutions of a rotary encoder, the amount of current a motor is drawing or the output of a strain gauge, as shown on the right in Fig.1. This information can then be fed back to the patient via various means, such as vibration (for example). In an electronically controlled prosthetic limb (Fig.2), proprioception information may be acquired as per the following example. 1. The prosthesis is activated by biological signals from the user, such as through surface electrodes to pick up nerve activity on the stump or a brain-computer interface such as Neuralink. 2. Proprioception information is acquired via sensors like strain gauges to measure deformation, rotary encoders to determine joint angle, limit switches and the amount of current drawn by a DC motor, which is related to its mechanical load. 3. This data is fed to a microprocessor and translated into information for position, movement, force and load. 4. This information is translated into a feedback signal for the user, such as (for example) some sort of amplitude or frequency modulated waveform that might represent angular position or torque. 5. The waveforms representing angular position and torque are sent to a ‘stimulator’ in the socket of the prosthetic device to create a sensation on the user’s skin or nerves. Devices to do this might cause skin stretch, vibration, electrical stimulation of nerves or the creation of a tendon-­vibration illusion (TVI), which generates a perception of joint motion. Sometimes, several proprioception siliconchip.com.au Fig.1: natural (left) and artificial (right) proprioception strategies. Source: www. researchgate.net/figure/fig1_373816713 Fig.2: artificial proprioception. Source: www.researchgate.net/figure/ fig2_373816713 methods can be used simultaneously to provide multi-channel feedback to the user. Prosthesis control Proprioception information and control of prosthetic devices may be Australia's electronics magazine achieved via the following means, which are either in use, under development or proposed. They involve either external sensors (such as capacitance measurement of the external environment) or sensing of residual muscle or nerve activity in a patient’s stump. March 2025  15 Servomotors Controlled prosthesis joint Agonist Channel 3 Reference Antagonist Residual limb Channel 1 Channel 2 Inductive powering system Wireless communication with both servomotors Channel 4 Fig.3: a proposed cineplastic procedure to sense forces on a muscle pair (agonist and antagonist) to control a prosthesis. Source: Control Methods for Transradial Prostheses Based on Remnant Muscle Activity and Its Relationship with Proprioceptive Feedback; siliconchip.au/link/ac3s Fig.4: a possible arrangement of EMG electrodes on a healthy forearm. A similar arrangement would be used in the case of a missing hand. Some of these methods are more accurate than others, while some are subject to noise. Both of these problems can be improved by a combination of approaches. Some may turn out to be impractical. Capacitance sensing is a method to measure the distance to nearby conductive objects using a pair of electrodes, with the electrodes excited by a sinewave at several hundred kilohertz (kHz). As a conductive object is moved closer to the electrodes, the amplitude of the excitation signal is modulated, indicating the distance. The closer the object, the greater the amplitude. Cineplasty (Fig.3) is an old surgical approach to altering residual limb muscle to enable a mechanical connection to control a prosthesis. It has several disadvantages, but a modern proposed conceptual approach involves connecting servomotors at ends of muscle pairs with wireless communication to and from a prosthesis. Electrical impedance tomography (EIT) involves wrapping a series of electrodes around a residual limb, like a forearm, and measuring the electrical impedance between electrodes. Information thus obtained can be used to infer user intent and a prosthetic device such as a hand can be controlled. Electromyography (EMG) is the most common method in use today to control prosthetic devices. It involves interpreting nervous system signals within residual muscles. An EMG signal has a voltage of around 1-10mV and a frequency up to 500Hz. Typically, EMG signals are measured on the skin surface, but electrodes can also be implanted for this purpose. Fig.4 shows a possible arrangement of multiple EMG electrodes on intention to operate a prosthesis, although this approach seems impractical for a variety of reasons. Phonomyography is a method of detecting muscle activity by its emission of low-frequency oscillations (5-100Hz) during contraction. They can be detected using acoustic means, such as by microphones or accelerometers placed in contact with the skin. Sonomyography uses ultrasound to monitor muscle movement in a stump. This can be used to interpret patient intention to control a prosthetic device. 16 Silicon Chip the skin surface of a healthy forearm. Force myography consists of attaching an array of force sensors on a residual stump to determine patient intention to move a prosthetic device by their activation of the remaining muscles. Magnetomyography is a method of measuring nerve system electrical signals in the stump by detecting extremely small magnetic fields using such devices as SQUIDs (superconducting quantum interference devices). Such methods are certainly impractical in a portable device at the moment. Myokinetics is a proposed procedure in which magnets are implanted in the residual muscles of a forearm. A three-axis magnetic field sensor is wrapped around the surface of the limb to control a prosthetic hand as the muscles are activated by the patient. Near-infrared spectroscopy using light at wavelengths of 760nm and 850nm can detect oxygenated and deoxygenated haemoglobin in the bloodstream. This can be used as a proxy to monitor muscular contractions. Human tissue is somewhat transparent to these wavelengths and so, as the amount of oxygenated blood changes in muscle as they relax or contract, it is possible to monitor muscle movement. If the residual muscles of a stump are monitored using a separate near-infrared transmitter and receiver in contact with the skin surface, it is possible to infer patient intention to control a prosthetic device. Optical myography is an approach whereby high-resolution imaging is used to look for changes in the shape of a stump due to skin deformation caused by underlying muscle activity. This can indicate the patient’s Australia's electronics magazine Commercial prostheses Some commercial electronically controlled prosthetic limb devices are as follows: Blatchford Intelligent Prosthesis The first commercially available microprocessor-controlled artificial limb was the Blatchford Intelligent Prosthesis, released in 1993 by UK company Blatchford Mobility. This was a leg with an articulated knee design, which was programmed to suit individual users and enabled a smooth, energy efficient gait pattern. It did this by determining walking speed and allowing the appropriate amount of swing phase extension. Unfortunately, we can’t find any good photos of the device. Bebionic Myoelectric Hand Bebionic (www.ottobock.com/ en-au/home) makes an artificial hand, shown in Fig.5, which is myoelectrically controlled by nerve signals picked up from skin electrodes on the residual limb. It can be coupled with arm components if the forearm or upper arm is also missing. siliconchip.com.au It is controlled by electrodes contained within a forearm enclosure, which pick up myoelectric signals from the residual forearm. This prosthesis uses Myo Plus pattern recognition and machine learning to interpret user intent. Luke Arm The Luke Arm (mobiusbionics.com/ luke-arm) is a prosthetic arm inspired by the prosthetic hand attached to Luke Skywalker from the movie Star Wars: A New Hope (1977) – see Fig.6. It is only available in the United States. It is of modular construction and is available in three lengths (transradial, transhumeral and shoulder disarticulation), depending on the extent of the arm or hand amputation. In the longest version, it has ten powered degrees of freedom, including a powered shoulder, humeral rotator and wrist flexor with ulnar/radial deviation. In addition, the hand component has multiple preprogrammed positions with grip force feedback. The company states that it is the only commercially available prosthesis with a powered shoulder. The transradial version weighs 1.4kg, transhumeral 3.4kg and shoulder disarticulation 4.7kg. The prosthesis has multiple control options, such as with pressure switches, rocker switches or myoelectric electrodes. It can also make use of inertial measurement units worn on the shoes to translate foot movement to a specific hand/arm action controlled by movement of the toe, heel, inside or outside of the foot. The forearm of the device has lights that indicate to the wearer hand or arm mode, current grip selection, battery levels, low battery icons and faults. There is also an optional feature called Tactor, which provides alerts and sensory feedback such as for grip force, via vibration. Open Bionics Open Bionics (https://openbionics. com, not to be confused with https:// openbionics.org) makes relatively inexpensive 3D printed arms and other prosthetics. The Hero Arm product, designed for those missing a forearm but who have a remaining elbow, has a hand with a gripping capability with six different grip types and is available in a variety of sizes, including one to suit children over eight years. siliconchip.com.au Fig.6: the longest version of the Luke Arm, inspired by Star Wars. Source: https:// mobiusbionics. com/luke-arm Fig.5: the Bebionic EQD hand. Each finger has individual motors and there are 14 different grips and hand positions available. Skin-coloured “gloves” are available to cover the hand. Source: www.ottobock.com/enus/product/8E70 Fig.7: the Open Bionics Hero Arm. Source: https://openbionics. com/hero-armoverview Fig.9: the Össur microprocessorcontrolled waterproof Proprio Foot. Source: www. ossur.com/enus/prosthetics/ feet/propriofoot Fig.8: the Össur i-Limb Quantum “multi-articulating myoelectric hand prosthesis” hand. This model has titanium digits for increased grip force and strength. Source: www. ossur.com/en-us/ prosthetics/arms/ilimb-quantum It is operated by picking up nerve signals from the stump. Interestingly, it can be customised with various different covers with different designs, including a Spider-Man design for children – see Fig.7. Several videos of it in action can be seen at https:// openbionics.com/how-to-use-a-heroarm showing operation of the arm for some common tasks. Össur i-Limb Quantum Hand & Proprio Foot Össur (www.ossur.com/en-us) makes various products including prosthetics, such as partial and full hands, feet and waterproof prosthetic legs, as well as others. Two products of note are a myoelectric controlled hand prosthesis (see Fig.8) and a microprocessor-controlled foot prosthesis (Fig.9). PSYONIC Ability Hand The PSYONIC Ability Hand (www. psyonic.io/ability-hand) promotes itself as the “world’s fastest, incredibly Australia's electronics magazine durable, and first ever touch-sensing bionic hand” (see Fig.10). It has sensors that detect grip pressure and provide user feedback via vibration. It is also designed to be strong and water resistant. Up to 32 different grip patterns are available. It is charged via a USB-C and a charge lasts about 6–8 hours of use. It is operated by myoelectric sensing of nerve system activity in the residual limb, as well as force-sensitive resistors and linear transducers from third parties. The Ability Hand can also be fitted to robots – see Fig.11. Utah Bionic Leg The Utah Bionic Leg (www. Fig.10: the PSYONIC Ability Hand. Source: PSYONIC user manual; siliconchip.au/link/ac3q March 2025  17 ◀ Fig.11: a NASA humanoid robot and a person both fitted with PSYONIC Ability Hands. Source: www.psyonic. io/robots Fig.12: the Utah Bionic Leg. Source: www.mech.utah.edu/utah-bionic-legin-science-robotics mech.utah.edu/utah-bionic-leg) is under development at the University of Utah – see Fig.12. It is designed for lower-­leg amputees. It is lightweight, using artificial intelligence and a variety of sensors for determining torque and acceleration and the prosthesis’ position in space. It can adapt to a variety of different walking activities. It does not use significant power for walking on level ground, so it can be used almost indefinitely on such terrain. During such activity, the battery is recharged upon limb deceleration, similar to regenerative charging in an electric vehicle (EV). Open-source prostheses There are several open source prosthetic limb projects as follows: OpenBionics OpenBionics (https://openbionics. org) describes itself as an open-source initiative that develops “affordable, light-weight, modular, adaptive robotic and bionic devices that can be easily reproduced using off-the-shelf materials”. It derives its original inspiration from the Yale Open Hand Project, described below. One of OpenBionics’ developments is shown in Fig.13. Open Source Leg The Open Source Leg (www.­ opensourceleg.org) project has a mission to develop standardised hardware and software platforms for prosthetic legs and to encourage worldwide cooperation from researchers in the field. In particular, it is to help develop appropriate control strategies to operate the legs (see Fig.14). It is not specifically intended as a user leg, but rather it is for researchers. The platform runs a Raspberry Pi computer. The website contains all the information necessary to enable researchers (or even Silicon Chip readers!) to build their own prosthetic leg. The cost is estimated at US$900019000, which is much cheaper than commercial devices. You can see the detailed costings at www.opensourceleg.org/build/make and a video on it at https://youtu.be/ xFliFk65l3Q The Yale OpenHand project The purpose of the Yale OpenHand Project (www.eng.yale.edu/grablab/ openhand) is to make low-cost, opensource robotic hands (see Fig.15). It is mentioned that a purpose of the project is to “make prosthetic hands more widely available through the lowering of costs” (siliconchip.au/ link/ac3r). We see no reason that these hands could not be incorporated into prosthetic limbs. Fig.13: the OpenBionics hand model. Source: https://openbionics.org/ affordableprosthetichands 18 Silicon Chip Australia's electronics magazine siliconchip.com.au Exoskeletons A powered exoskeleton is a wearable machine that covers all or part of a wearer’s body and interprets their intended motion and moves accordingly. They have a variety of uses in the military and industry, to assist the carrying of heavy loads or to relieve users of possible repetitive strain injuries. They can also be used to assist the paralysed, or those with muscle weakness or infirmity, to walk. They have uses in rehabilitation too. We will look at some powered exoskeleton devices that assist people who have trouble walking. Cyberdyne Hybrid Assistive Limb The Hybrid Assistive Limb (www. cyberdyne.jp/english/products/HAL) is a joint development between Japan’s Tsukuba University and the robotics company Cyberdyne. The lower body version is shown in Fig.16 and helps the partially paralysed (where some residual nerve function still exists in the legs) or infirm to walk. The device has sensors that are attached to a patient’s flexor and extensor muscles that detect and interpret electrical signals from nerves. There are four motorised joints, one for each hip and knee. It is available as a single- or dual-leg model, weighing 9kg or 14kg respectively, with an operating time of about one hour. EksoNR by Esko Bionics The EksoNR (Fig.17) is an exoskeleton device designed to assist in the rehabilitation of patients in a clinical setting with physical therapists. It is suitable for conditions such as acquired brain injury, stroke, multiple sclerosis (MS) and spinal cord injury, and is designed to re-teach the brain and muscles how to walk again. Figs.16-18 (left-to-right): the Cyberdyne Hybrid Assistive Limb; EksoNR exoskeleton; and the HANK lower limb exoskeleton. Sources: www.cyberdyne. eu/en/products/medical-device/hal-limb & https://eksobionics.com/eksonr & www.gogoa.eu/en/exoesqueletos-medicos-hank It can work with software called GaitCoach, which alerts therapists to any aspect of the patient’s gait that needs correction and further training. The device weighs about 27kg. See https://youtu.be/RtBaQEKcguk HANK by Gogoa Mobility H A N K ( w w w. g o g o a . e u / e n / exoesqueletos-medicos-hank) is a lower limb exoskeleton intended for rehabilitation of patients with spinal cord injuries, neurodegenerative disorders and who have had brain injuries (see Fig.18). WalkON Suit F1 exoskeleton Korea Advanced Institute of Science and Technology (KAIST, www.kaist. ac.kr) of South Korea makes the WalkON Suit F1, developed jointly with Angel Robotics (https://angel-robotics.­ com/en). It is described as a wearable robot for paraplegics. The F1 can walk independently up to a user sitting in a wheelchair, after which the user attaches the device. The F1 learns an optimal walking strategy for each user based on weight and balance considerations using a neural network. See Fig.19 and the video at https://youtu.be/ kQ2fSap1E2I This suit and its research team won a gold medal at the 2024 Cybathlon (described later in text). Fig.14: the Open Source Leg. It is designed for researchers to develop control software for prosthetic legs. Source: www.opensourceleg.org/ build/make Fig.15: an open-source robotic hand at the end of a robotic arm, from the Yale OpenHand project, which could be incorporated into a prosthesis. Source: www.eng.yale.edu/grablab/ openhand siliconchip.com.au Australia's electronics magazine March 2025  19 ReWalk exoskeleton ReWalk is a “personal robotic exoskeleton” from Israel (https:// golifeward.com) that allows paralysed patients to walk again (see Fig.20). Patients strap themselves into the device and it provides powered hip and knee motion to walk, turn, negotiate curbs and climb stairs. It uses a computer-based control system and motion sensors to mimic walking. Fig.19: the WalkON Suit F1 for paraplegics. Source: https://angelrobotics.com/en/products/suit/ walkon-suit.php Walking Assist Device by Honda Although it doesn’t appear to be currently on the market, the Walking Assist Device by Honda (the car company) was designed to help patients with impaired walking function who are unable to walk unassisted, for example, stroke victims or those with muscular weakness. It consists of an exoskeleton-type device with attachments via straps at the hip and thighs and it weighs only 2.7kg (see Fig.21). It is, or was, an offshoot of Honda’s walking robot research. Wandercraft Wandercraft (en.wandercraft.eu) makes the Atalante X exoskeleton device to assist paraplegics to become uprightly mobile again. Unlike most other exoskeleton devices, it does not need handheld poles, and is thus hands-free – see Fig.22. Brain interfaces Fig.20: the ReWalk Personal Exoskeleton allows paralysed patients with spinal cord injuries to walk again. Source: https://golifeward. com/products/rewalkpersonalexoskeleton Fig.21: Honda’s Walking Assist Device. Source: https://assets. blackxperience.com/content/ blackauto/autonews/walk-assist-back-view-3.jpg 20 Silicon Chip Fig.22: the Wandercraft Atalante X hands-free exoskeleton for paraplegic patients. This patient is being trained, hence the overhead support strap. Source: https://en.wandercraft.eu An alternative strategy to sensing myoelectric impulses on the skin surface or other methods is to control prosthetic limbs via a direct brain-computer interface. A complete system (Fig.23) consists of the electrode array, a neural signal processor and software. A video of a patient using the device to move robotic arm can be seen at https:// youtu.be/QRt8QCx3BCo BrainGate BrainGate’s by-line is “turning thought into action” (www.braingate.­ org). This research organisation has developed an experimental brain-­ computer interface implant to interpret electrical activity at specific brain locations to assist patients with conditions such as amyotrophic lateral sclerosis (ALS) or spinal cord injury. This allows them to control artificial limbs or operate computers. It uses an electrode system known as the Utah Array, also called the NeuroPort Electrode, which is commercially available for experimental purposes from Blackrock Neurotech (https:// blackrockneurotech.com/products/ utah-array). Neuralink Elon Musk’s company Neuralink (https://neuralink.com) is developing a brain-computer interface (BCI) device to transform a person’s thoughts into actions by a computer or other device – see Fig.24. Neuralink can potentially control wheelchairs, robotic exoskeletons and artificial limbs by thought alone. The amazing potential for Neuralink to control external devices is shown in the following video, in which a monkey with two Neuralink devices installed plays “MindPong” using its thoughts alone: https://youtu.be/­ rsCul1sp4hQ Neuralink is running a clinical trial called “Precise Robotically Implanted Australia's electronics magazine siliconchip.com.au Fig.23: the Blackrock brain-computer interface system with the Utah Array (Neuroport Electrode array) shown insert. Source: https://blackrockneurotech. com/our-tech Fig.24: an exploded diagram of Neuralink. Source: https:// drkaushikram.com/wp-content/ uploads/2023/07/Neuralink.jpeg Brain-Computer Interface (PRIME) study”. It “aims to evaluate the safety and effectiveness of its BCI implant, the N1, along with the surgical robot R1 and the N1 User App”. The implant will have 1024 electrodes. The first human with a Neuralink chip installed has used it to move a cursor to play chess. You can see this in the video at https://youtu.be/­ 5SrpYZum4Nk load-bearing prosthetic limbs is called osseointegration. In both cases, the body interprets them as foreign bodies and mounts an aggressive immune system attack to isolate or expel them. It is thus vitally important to use the most biocompatible materials possible, such as titanium, certain ceramics such as zirconia, and silicone. Still, even these materials are recognised as foreign by the immune system. When such penetrations are made, they can be prone to infection and sometimes have to be removed. Nevertheless, advances in these techniques have been made. Note that osseointegration of prosthetic components such as hip and knee joints is already done routinely and effectively. The difference with prosthetic limbs is the externalisation of the implant through the skin, which creates many additional challenges. Tooth implants with the support structure externalised through the gum are generally successful, although the mouth is more resistant to infection than the skin. Fig.26: a patient with a prosthetic leg attached to their body using the OPRA osseointegration system. Source: https://integrum.se/about-us/ourtechnology/opra-implant-system Fig.27: a patient with an experimental e-OPRA prosthetic limb who can complete challenging tasks as a truck driver. Source: https://integrum.se/ about-us/our-technology/e-opra Transcutaneous penetrations and skeletal attachments Two of the most challenging and related areas of prosthetic devices are the transcutaneous (through-skin) penetrations of tubes and wires, and direct skeletal attachment of prosthetic limbs. Direct skeletal attachment of The OPRA implant system Integrum (https://integrum.se) is a Swedish company that has developed the OPRA implant system for osseointegration of prosthetic limbs. There are two different versions of OPRA: one is commercially available, while another, called e-OPRA, is experimental. Fig.25 shows the method by which the OPRA implant is attached to bone and externalised through the skin. A patient with a prosthesis attached via the OPRA system is shown in Fig.26. Bone Fixture Skin Abutment Abutment Screw Fig.25: details of the OPRA implant system. Source: https://integrum. se/about-us/our-technology/opraimplant-system/transfemoral-aboveknee-amputations siliconchip.com.au Australia's electronics magazine March 2025  21 The experimental e-OPRA system is connected directly to the body’s nervous system rather than sensing electrodes on the skin, as shown in Figs.27-29. Cybathlon Cybathlon (https://cybathlon.com/ en) is a competitive event for teams from all over the world that develop assistive technologies – see Fig.30. There is a video of highlights from the 2024 Cybathlon viewable at https:// youtu.be/WbhvEbVW1-I Such events encourage the development and use of new prosthetic technologies. Limb regeneration or transplanting Though not the main topic of discussion here, there are alternatives to prosthetic limbs. Rather than having an artificial limb, the ultimate solution would be to regrow an entire new body part. This process already occurs with some animals like salamanders, so it is at least possible in principle. If their leg is cut off, they will regrow it. It is believed that limb regrowth is at least theoretically possible in humans. It is a matter of activating the right biological pathways to enable it to happen, and many researchers are investigating this. An Australian scientist, Dr James Godwin, discovered that in humans, the scarring that occurs due to a significant wound actually prevents limb regeneration. If scarring could be prevented, perhaps limb regeneration would occur. There is also a substance called ‘extracellular matrix’, one variety of which has been called “pixie dust”, that has been shown to produce tissue regeneration in humans with some success. With advances in management of tissue rejection and surgical techniques, limb transplants, such as hands, arms and legs have been performed. Another approach is the ‘biolimb’. A biolimb is created when a donor limb has its cells removed, leaving behind just the collagen supporting matrix. This is then repopulated with cells from the intended recipient such as nerves, muscles, blood vessels and skin tissues. These are placed into the appropriate areas. 22 Silicon Chip This has been done for more simple body parts, such as windpipes, with varying levels of success. With a limb, there are numerous tissue types to populate, so the process is much more complicated. As no tissue remains of the donor that could be recognised as foreign by the recipient, there are no problems with rejection or having to take lifelong immunosuppressive drugs. Further reading Enabling the Future (https://­ enablingthefuture.org) is a global network of citizen volunteers who use their 3D printers to make opensource upper limb designs to assist Fig.28: an e-OPRA osseointegration system. The abutment is where the prosthetic limb is attached, and there are connections to nerves and muscle tissue. Source: https://integrum.se/ about-us/our-technology/e-opra children and adults in need. They are mainly for those born without fingers or hands, or who have lost them due to war, natural disasters, illness or accidents. Instructions on how to get involved are at https://enablingthefuture.org/ learn-more-get-involved Some companies are partnered with a wide range of prosthetic manufacturers and also perform customisation to help formulate a solution for most types of amputees. One US company we saw was A Step Ahead Prosthetics (www.weareastepahead. com). You can watch a YouTube video about them at: https://youtu. SC be/KDMbJOTXNrw Fig.29: with the e-OPRA system, control and sensory information is transmitted by nerves from (blue line) and to (green line) the brain. Sensory information from the prosthesis provides a sense of feel. Source: https://integrum.se/about-us/ourtechnology/e-opra Fig.30: a competitor with a prosthetic leg completes a task at Cybathlon 2024. Source: https://cybathlon.com/en/events/edition/cybathlon-202 Australia's electronics magazine siliconchip.com.au